This invention relates to an automatic welding apparatus in which an industrial robot is used for performing welding.
Welding is one of the sections of industry in which the need for automation is most keenly felt to dispense with manual labor, because welding workers in their workshops must work under conditions which are harmful to health due to gases produced when welding is performed. Many attempts have, therefore, been made in recent years to introduce automatic operation into the field of welding by using an industrial robot.
Man is endowed with a highly developed brain and organs of senses, such as visual, tacticle and olefactory, and his body is soft and flexible. These qualities enable man to perform a highly complicated operation without any difficulty. When attempts are made to let a robot or other machine replace man in performing an operation automatically without manual attention, one invariably finds how difficult it is to let the machine perform an operation which is very simple for man to perform. This is particularly true with automation of a welding operation. A robot or other machine, although capable of faithfully performing an operation repeatedly with a high degree of precision so long as the operation is planned beforehand, lacks versatility because it is unable to make a decision by itself and alter the contents of the operation. This is one of the important problems encountered in automation of a welding operation.
More specifically, when alterations are made in the contents of an operation, new contents of the operation must be taught to the machine item by item. In a welding operation, components to be welded into a unitary structure are usually low in dimensional and configurational accuracy and this results in the contents of the operation differing from one set of components to another. This had made it necessary for the operator to teach the machine new contents of the operation for each set of components to be joined by welding. This is time consuming and requires a lot of labor in teaching the new contents to the machine. Thus, although the use of a robot or other machine in performing a welding operation has the effect of preventing workers from working under unhealthy conditions, it does not meet the requirement of economizing on labor. It will be appreciated that the most important problem encountered in automating a welding operation is how to enable a welding operation to be performed without requiring to teach the machine new contents of the operation each time alterations are made in the operation.
In order to solve this problem, efforts have been made to increase the dimensional and configurational precision of the components to be welded into a unitary structure to make up for the lack of ability of a robot, so that the need to teach the contents of the operation to the robot for each set of components to be welded can be eliminated. This requires cutting of steel plates accurately in accordance with the design drawing. Steel plates must be cut by a new process as by using a plasma, not a gas, so that the dimensions of the components when temporarily assembled are correct with a tolerance of .+-. 1 mm. When a gas is relied on for performing cutting of steel plates, it will be necessary to use an NC machine tool.
It will also be necessary to perform temporary assembling of components, which has hitherto been performed by means of simple gages and jigs, by using mechanized equipment in order to increase the precision with which assembling is accomplished.
A great deal of efforts are required in accurately positioning the temporarily assembled components on the positioner in the next following step of operation. Even if a lot of time and labor are devoted to the operation of positioning the temporarily assembled components prior to welding them into a unitary structure, the occurrence of welding deformation is unavoidable during the welding operation. Thus, the weld made may be deflected considerably from the predetermined position due to welding deformation as the welding operation draws to a close. In the prior art method, it is impossible to absorb the deflection of the weld due to welding deformation. If the components are welded in a position other than the position planned for welding, the strength of the welded structure will be greatly lowered or a lot of time and labor will be required for performing repair. Also, many accidents, such as collision of the welding torch against the components to be welded, will cause damage to the welding machine or the robot, and a short circuit accident will also occur.
As aforesaid, automatic welding apparatus of the prior art, although enabling manual attention to be eliminated in acutally performing welding because of the fact that welding itself is performed by a robot, has the disadvantages of having to perform time-consuming preparatory operations by a large number of operators prior to a welding operation or of requiring additional equipment. Thus, full realization of advantages from use of a robot in performing an automatic welding operation has been hampered by inability to overcome these obstacles.